Reactor internal structure and method of manufacturing the same

ABSTRACT

A coating of niobium oxide, zirconium titanate, or nickel titanate is formed on at least a part of a surface of a jet pump member constituting a jet pump serving as a reactor internal structure of a boiling water reactor. Further, a solution containing, e.g., a niobium compound is applied to at least a part of the surface of the jet pump member constituting the jet pump, and the jet pump member coated with the solution is heat-treated to form a coating of, e.g., niobium oxide. With this configuration, the jet pump member constituting the jet pump of the boiling water reactor is provided such that deposition of crud can be sufficiently suppressed on the jet pump member.

TECHNICAL FIELD

The present invention relates to a reactor internal structureconstituting a boiling water reactor and a method of manufacturing thesame, and particularly, to a reactor internal structure and a method ofmanufacturing the same which can suppress deposition of crud on thereactor internal structure.

BACKGROUND ART

In a boiling water reactor, a jet pump system is adopted to increasepower density. The jet pump system forcibly circulates reactor coolantas cooling water and includes an external recirculating system and aninternal recirculating system as systems for forcibly circulatingreactor coolant through a core portion of a reactor pressure vessel.

The external recirculating system includes a plurality of jet pumps in areactor pressure vessel and a recirculating pump outside the reactorpressure vessel. Cooling water fed from the recirculating pump is jettedby the jet pumps and reactor water around the jet pumps is drawn andforcibly fed into a core portion from a core bottom plenum disposedunder the core portion, so that the reactor coolant is forciblyrecirculated in the reactor pressure vessel.

FIG. 1 is a vertical cross-sectional view schematically showing aconfiguration of a boiling water reactor in which a jet pump system ofthe external recirculating system is adopted. A reactor pressure vessel1 contains reactor coolant 2 and a core 3. The core 3 includes aplurality of fuel assemblies and control rods, not shown, and is housedin a core shroud 10.

The reactor coolant 2 passes through the core 3 upward and issimultaneously heated by nuclear reaction heat of the core 3 and thenbecomes a two-phase flow of water and steam. The coolant 2 in thetwo-phase state flow into a steam separator 4 installed above the core 3and is separated into water and steam. The steam is introduced into asteam dryer 5 above the steam separator 4 to obtain dry steam, and thedry steam is transferred into a steam turbine, not shown, through a mainsteam line 6 and is used for power generation. A downcomer 7 between thecore shroud 10 and the reactor pressure vessel 1 contains a plurality ofjet pumps 11 spaced at regular intervals in a circumferential direction.The water separated by the steam separator 4 is pressurized through arecirculation system, not shown, is introduced into the jet pumps 11from recirculation inlet nozzles 13, and flows under the core 3 throughthe jet pumps 11.

FIG. 2 is an enlarged perspective view showing a principle part of thejet pump 11 of FIG. 1. As shown in FIG. 2, the jet pump 11 includes avertical riser tube 12 that introduces the coolant 2, which has beensupplied from the recirculation inlet nozzle 13 of a recirculating pump,not shown, as an upward flow inside the reactor. The upper part of theriser tube 12 is connected to a pair of elbows 15 via a transition piece14. The elbows 15 split the coolant into two downward flows. The elbows15 are each connected to an inlet throat 17 via a mixing nozzle 16. Themixing nozzle 16 discharges the coolant 2 and surrounding reactor wateris drawn with the coolant 2. The discharged coolant 2 and the drawnreactor water are mixed in the inlet throat 17. The inlet throats 17 areeach connected to a diffuser 18 that feeds the coolant below the core.The elbow 15, the mixing nozzle 16, and the inlet throat 17 areintegrated into a single unit called inlet mixer 51.

In the case of jet pumps constituting a boiling water reactor,unfortunately, crud of iron oxide in the reactor water is deposited andbuilds up on surfaces of jet pump members constituting the jet pump,which increases a pressure loss and reduces a flow rate, resulting inlower circulation efficiency. The components of the reactor internalstructure provides like or similar problem. For example, crud (CRUD:Chalk River Unclassified Deposit) is considerably deposited and buildsup on the jet pump members constituting the inlet mixer exposed to ahigh flow rate of hot water.

This matter has been dealt with at present by increasing the speeds ofrecirculating pumps (PLR pumps), which however has caused a large energyloss.

Further, although a water jet cleaning method has been also proposed toremove the deposited crud, this involves extremely high cost, thus beingnot practical.

Moreover, formation of a coating on surfaces of jet pump members hasbeen proposed to suppress deposition of crud on reactor internalstructures including the jet pump members. For example, in methodsproposed in specifications of Japanese Patent Laid-Open No. 2002-207094(Patent Document 1) and U.S. Pat. No. 6,633,623 (Patent Document 2),coatings of oxides including TiO₂, ZrO₂, TaO₂O₅, and SiO₂ are formed onsurfaces of the jet pump members by a CVD (chemical vapor deposition)method or process. Further, in methods proposed in specifications ofJapanese Patent Laid-Open No. 2007-10668 (Patent Document 3) and U.S.Patent Application Publication No. 2007/0003001 (Patent Document 4),coatings of platinum, rhodium, iridium, palladium, silver, and gold ormetal alloys thereof are formed on surfaces of component parts such asjet pump members by methods or means of, e.g., plasma spray coating,HVOF, CVD, PVD, electroplating, and electroless plating.

As mentioned above, in reactor internal structures such as jet pumps ofa boiling water reactor, the crud in reactor water is deposited andbuilds up on, e.g., surfaces of jet pump members constituting thereactor internal structures, which might increase a pressure loss and aflow rate, resulting in lower circulation efficiency. In order toimprove this matter, it has been proposed, in a conventional technology,to form coatings on the surfaces of the jet pump members to therebysuppress adhesion of deposited crud such as disclosed in the related art(Patent Documents 1 to 4). In these proposals, however, deposition ofcrud cannot be sufficiently suppressed by forming the coatings.Moreover, the formation of the coatings requires an expensive apparatus,and size and shape of members to be coated are limited.

DISCLOSURE OF THE INVENTION

The present invention has been conceived to solve the defective mattersdescribed above, and an object of the present invention is to provide areactor internal structure that can sufficiently suppress deposition ofcrud on a reactor internal structure of a boiling water reactor.

Another object of the present invention is to provide a method ofinexpensively manufacturing a reactor internal structure that cansufficiently suppress deposition of crud with a simple manufacturingprocess and is applicable to a complexly shaped member or a large-sizedmember.

The inventors of the present invention have earnestly studiedsuppression of deposition of crud on a reactor internal structure of aboiling water reactor, and as a result, the inventors found thatdeposition of crud can be suppressed by forming a coating of niobiumoxide, zirconium titanate, or nickel titanate and also found that ahigh-quality coating of niobium oxide, zirconium titanate, or nickeltitanate can be inexpensively formed by so-called chemical solutiondeposition including the steps of: applying a solution containing acompound of these metals to the surface of the reactor internalstructure; and forming a coating by heat-treating the reactor internalstructure coated with these solutions. Thus, the present invention hasbeen completed.

A reactor internal structure according to the present invention is areactor internal structure constituting a boiling water reactor, thereactor internal structure having a surface at least partially coatedwith niobium oxide, zirconium titanate, or nickel titanate.

A method of manufacturing the reactor internal structure according tothe present invention includes the steps of: applying a solutioncontaining a niobium compound to at least a part of a surface of thereactor internal structure constituting the boiling water reactor; andforming a coating of niobium oxide by heat-treating the surface of thereactor internal structure coated with the solution.

A method of manufacturing a reactor internal structure according to thepresent invention includes the steps of: applying a titanium-zirconiumcompound solution to at least a part of a surface of the reactorinternal structure constituting a boiling water reactor; and forming acoating of zirconium titanate by heat-treating the surface of thereactor internal structure coated with the solution.

A method of manufacturing a reactor internal structure according to thepresent invention includes the steps of: applying a titanium-nickelcompound solution to at least a part of a surface of the reactorinternal structure constituting a boiling water reactor; and forming acoating of nickel titanate by heat-treating the surface of the reactorinternal structure coated with the solution.

According to the present invention, it is possible to suppressdeposition and buildup of crud on a surface of the member of the reactorinternal structure constituting the boiling water reactor, therebykeeping initial performance of coolant passing through the reactor.Moreover, according to the manufacturing method of the presentinvention, the reactor internal structure capable of sufficientlysuppressing deposition of crud can be manufactured with a simplemanufacturing process at low manufacturing cost.

BRIEF DESCRIPTION OF THE DRAWINGS

[FIG. 1] is a vertical cross-sectional view schematically showing aconfiguration of a boiling water reactor in which a jet pump system ofan external recirculating system is adopted.

[FIG. 2] is an enlarged perspective view showing an essential part of ajet pump 11 of FIG. 1.

BEST MODE FOR CARRYING OUT THE INVENTION

In the following, there will be described an example in which anembodiment of the present invention is applied to a jet pump serving asa reactor internal structure of a boiling water reactor. In the presentdisclosure, terms representing directions, such as “upper”, “lower”,“right”, “left” and so on, represent directions are used with referenceto the illustration in the drawings or in an actual installation stateof the reactor.

As described above, FIG. 2 is an enlarged perspective view showing anessential portion of a jet pump 11 of the boiling water reactor. Inorder to suppress deposition of crud on the jet pump 11, a coating ofniobium oxide, zirconium titanate, or nickel titanate is formed on atleast a part of a surface of a jet pump member constituting the jet pump11, particularly, on a portion having much deposition of crud. Thus, itis possible to suppress the deposition and the build-up of the crud inthe reactor water on the surface of the jet pump member, thereby keepinginitial performance of the jet pump 11 for an extended period.

Although the deposition and build-up of the crud on the surface of thejet pump member can be suppressed by forming the coating, it is notclear whether such effects can be achieved by every mechanism or not,and the mechanism is assumed as follows.

First, a coating of niobium oxide, zirconium titanate, or nickeltitanate is formed on at least a part of the surface of the jet pumpmember, so that the surface of the jet pump member has a negativesurface potential. Meanwhile, iron oxides such as hematite (Fe₂O₃) andmagnetite (Fe₃O₄) in the crud in the reactor water also have a negativesurface potential, so that it is expected that an electrical repulsiveforce is generated between the surface of the jet pump member and thecrud in the reactor water, and the deposition and build-up of the crudcan be suppressed on the surface of the jet pump member.

The coating of niobium oxide, zirconium titanate, or nickel titanate isstabilized and is not melted in reactor water of an actual nuclear powerplant, and moreover, oxidation resistance of a metal substrate isexpected to improve in addition to the suppression of the deposition andbuildup of the crud. Moreover, a coating having high adhesive strengthto the metal substrate can be formed by so-called chemical solutiondeposition.

It is preferred that the coating has a thickness of 0.01 μm to 10 μm.The thickness of the coating is set at 0.01 μm to 10 μm for thefollowing reason:

That is, in the case where the thickness of the coating is smaller than0.01 μm, the coating cannot evenly cover the substrate and the substrateis partially exposed, so that the oxidation resistance of the substraterapidly decreases. On the other hand, in the case where the thickness ofthe coating is larger than 10 μm, the adhesive strength of the coatingto the substrate decreases, so that cracks may occur on the coating, thesubstrate becomes less resistant to oxidation, and the coating may bepeeled off from the substrate.

In an actual nuclear power plant, the crud to the jet pump isconsiderably deposited and builds up on an inner surface of an inletmixer 51 that is exposed to a high flow rate of hot water. Accordingly,the formation of the coating is particularly effective on the innersurfaces of the jet pump members constituting the inlet mixer 51, forexample, a mixing nozzle 16 and an inlet throat 17.

Hereunder, a method of manufacturing the jet pump members according tothe present invention will be described.

In order to form the coating on the surfaces of the jet pump members,first, a solution containing a niobium compound, a titanium-zirconiumcompound solution, or a titanium-nickel compound solution is applied tothe surfaces of the jet pump members. Next, the jet pump members coatedwith these solutions are heat-treated to form a coating of niobiumoxide, zirconium titanate, or nickel titanate.

In this case, the solution containing the niobium compound, thetitanium-zirconium compound solution, or the titanium-nickel compoundsolution is, for example, a solution containing a complex of thesemetallic elements, a solution containing an alkoxide compound of thesemetallic elements, a solution containing salts of these metallicelements, and zol generated by hydrolysis on compounds of these metallicelements.

Solvents of these solutions include water, alcohols such as butanol andisopropyl alcohol, other organic solvents, and mixtures of thesesolvents.

The complex, the alkoxide compound, and the salts of these metallicelements are not particularly limited as long as the complex, thealkoxide compound, and the salts are soluble in the solvents. Thecompounds of metallic elements for generating the zol by hydrolysisinclude alkoxide compounds and salts. The compounds are not particularlylimited as long as the compounds are soluble in the solvents.

These solutions are applied to the surfaces of the jet pump members by,for example, dipping, spraying, spin-coating, roll-coating, bar-coatingand the like method. Optimal one of the methods may be adopted accordingto dimensions and shapes of the jet pump members to be coated.

Subsequently, the jet pump members coated with the solutions areheat-treated. The jet pump members coated with the solutions may be keptin an electric furnace and then entirely heated. Alternatively, only thesurfaces of the jet pump members may be heated by infrared radiation orany other radiation. The heating method is not particularly limited tosuch heating methods, and other known heating methods may be usedinstead.

The jet pump members are preferably heat-treated at 80° C. to 600° C. Aheat-treatment temperature lower than 80° C. causes problems such asinsufficient thermolysis of a niobium compound, a rough coating, and anunstable coating leading to aging and exfoliation. On the other hand, aheat-treatment temperature higher than 600° C. changes a structure of ametal serving as a substrate of the jet pump member, therebydeteriorating properties such as fatigue strength and creep strength. Aheat-treatment atmosphere contains oxygen in air.

The coating of niobium oxide, zirconium titanate, or nickel titanate isformed by the heat treatment on the surfaces of the jet pump members.

The method of manufacturing the jet pump members according to thepresent invention is so-called chemical solution deposition which is ahighly practical method inexpensively applicable to large jet pumpmembers or complexly shaped jet pump members with a simple processwithout the need for an expensive apparatus. Another advantage of themanufacturing method is that a coating can be evenly formed and surfaceroughness of the jet pump members hardly changes in a coating operation,thereby eliminating the need for processing after the coating operation.

In this example, although the present embodiment is applied to the jetpump, the present embodiment may be applied to reactor internalstructures including an inner surface of a core shroud, a stand pipe ofa steam separator, and a corrugated plate of a steam dryer. Further, inthis case, substantially the same effects are obtainable as thoseattained by the described embodiment.

First Example

As a test piece, there was prepared SUS304L stainless steel worked intoa rectangular test piece of 40 mm×5 mm×1 mm.

A 5-wt % butanol solution of niobium alkoxide was applied to a surfaceof the test piece by dipping and then the test piece was heat-treated at400° C. in atmosphere for ten minutes to form a coating. This processwas repeated three times to adjust a thickness of the coating.

The coating formed on the surface of the test piece had a thickness ofabout 1 μm and contained amorphous niobium oxide.

A crud deposition characteristic test that was a simulation of an actualnuclear power plant was performed to the test piece having the coating.

In the crud deposition characteristic test, the test piece is immersedand contained in water at 280° C. and 7 MPa and is kept therein for 300hours. The water contains crud of 60 ppm which is obtained by mixinghematite (Fe₂O₃) and magnetite (Fe₃O₄) in a ratio of 1 to 1. A cruddeposition characteristic is evaluated by measuring a change in a weightof the test piece before and after the test.

The test piece including the coating of amorphous niobium oxide formedwith a thickness of about 1 μm hardly varied in weight before and afterthe test.

Second Example

A coating was formed by the same method under the same conditions as inthe first example except for use of an isopropyl alcohol solutioncontaining 5 wt % of titanium-zirconium alkoxide in a one-to-one atomicratio of titanium to zirconium. The coating formed on a test piececontained amorphous zirconium titanate.

The test piece having the coating of zirconium titanate underwent a cruddeposition characteristic test by the same method as in the firstexample. As a result, the test piece hardly varied in weight before andafter the test.

Third Example

A coating was formed by the same method under the same conditions as inthe first example except for use of a butanol solution containing 5 wt %of titanium-nickel alkoxide in a one-to-one atomic ratio of titanium tonickel. The coating formed on a test piece contained amorphous nickeltitanate.

The test piece having the coating of nickel titanate underwent a cruddeposition characteristic test by the same method as in the firstexample. As a result, the test piece hardly varied in weight before andafter the test.

First Comparative Example

In a first comparative example, a crud deposition characteristic testwas performed to an uncoated test piece of a SUS304L substrate by thesame method as in the first example. As a result, large crud depositionwas observed on a surface of the test piece by a visual check ormicroscopy and a considerable weight gain was recognized.

As described above, it was confirmed that in the case where the reactorinternal structures including the jet pump members of the foregoingexamples are coated with niobium oxide, zirconium titanate, or nickeltitanate, deposition of crud can be effectively suppressed. Further, inthe method of manufacturing the reactor internal structures includingthe jet pump members of the foregoing examples, a high-quality coatingcan be inexpensively formed by chemical solution deposition regardlessof a shape and size of the reactor internal structure.

According to the present invention, it is therefore possible to suppressan increase in a pressure loss of a channel of a reactor internalstructure, e.g., a jet pump of a boiling reactor, and to hence stablymaintain initial performance for an extended period, thereby remarkablycontributing to safety of nuclear power plants.

1. A reactor internal structure constituting a boiling water reactor,the reactor internal structure having a surface at least partiallycoated with niobium oxide, zirconium titanate, or nickel titanate. 2.The reactor internal structure according to claim 1, wherein thezirconium titanate has a one-to-one atomic ratio of titanium tozirconium.
 3. The reactor internal structure according to claim 1,wherein the nickel titanate has a one-to-one atomic ratio of titanium tonickel.
 4. The reactor internal structure according to claim 1, whereinthe coating has a thickness of 0.01 μm to 10 μm.
 5. The reactor internalstructure according to claim 1, wherein the reactor internal structureis a jet pump member constituting an inlet mixer.
 6. A method ofmanufacturing a reactor internal structure, comprising the steps of:applying a solution containing a niobium compound to at least a part ofa surface of the reactor internal structure constituting a boiling waterreactor; and forming a coating of niobium oxide by heat-treating thesurface of the reactor internal structure coated with the solution.
 7. Amethod of manufacturing a reactor internal structure, comprising thesteps of: applying a titanium-zirconium compound solution to at least apart of a surface of the reactor internal structure constituting aboiling water reactor; and forming a coating of zirconium titanate byheat-treating the surface of the reactor internal structure coated withthe solution.
 8. The method of manufacturing a reactor internalstructure according to claim 7, wherein the titanium-zirconium compoundsolution has a one-to-one atomic ratio of titanium to zirconium.
 9. Amethod of manufacturing a reactor internal structure, comprising thesteps of: applying a titanium-nickel compound solution to at least apart of a surface of the reactor internal structure constituting aboiling water reactor; and forming a coating of nickel titanate byheat-treating the surface of the reactor internal structure coated withthe solution.
 10. The method of manufacturing a reactor internalstructure according to claim 9, wherein the titanium-nickel compoundsolution has a one-to-one atomic ratio of titanium to nickel.
 11. Themethod of manufacturing a reactor internal structure according to anyone of claims 6, 7, and 9, wherein the heat treatment is performed at80° C. to 600° C.
 12. The method of manufacturing a reactor internalstructure according to any one of claims 6, 7, and 9, wherein thecoating has a thickness of 0.01 μm to 10 μm.